Add annual frequency time option

We will likely also want to be able to process annual time frequency output for some components so adding support for that would be good. Already for land there are some variables on that frequency.

I'll try to have a crack at that shortly

Start by locating the existing frequency-processing logic and the land variables that already use annual frequency. Determine which components need annual output support and verify that those outputs are processed correctly across them.

Written by the indexing model from the issue text.